On Wed, 2011-08-24 at 13:46 -0700, Luck, Tony wrote:> > happen to remember what the perceived benefit of using> > __ARCH_WANT_UNLOCKED_CTXSW was about?> > No - digging around the code hasn't rung any bells for me either.> > Perhaps just general goodness for not holding a lock for> longer than we need to? But that would imply some case where> someone else could do something useful by being able to grab> the lock when we drop it. About the only thing I can think> of is that it would allow tasks to be re-balanced just a> teeny bit earlier --- but re-balancing ought to be somewhat> rare, yes?

Mostly yes, except remote wakeups, however that got a complete overhaulin 3.0. Instead of taking the remote rq->lock we now enqueue the task ona list and IPI the thing, then let the IPI do the remote enqueue andtrigger the reschedule.

So it might make sense to re-evaluate this on ia64 like Ken suggested..then again, who has a large ia64 box and is still willing to put timein?